In forestry, as known, working machines of various types are employed, which normally are wheeled and give rise to considerable lasting damages of the ground, for example in the form of deep wheel furrows. In order to prevent such ground damages, attempts have been made to manufacture endless-tracked forestry machines, but without appreciable success. This failing success has its reason to a large extent in the fact, that the tracks, which are particularly suitable for this purpose, viz. rubber tracks, which expose the ground to much less strain than, for example, steel tracks of the kind employed on excavators and the like, do not possess the tensile strength required for resisting the stresses they are subjected to when being mounted on known conventional track units.
The present invention, therefore, has the object of producing an improved track unit of bogie type, which renders it possible to distribute the driving force on several tracks of short length, and which shall be designed so as to permit the tracks to the greatest possible extent to follow the ground surface without being appreciably affected by the other tracks, even when these move over an obstacle in the form of a stone, stump or the like.
This primary object of the present invention is achieved in that the track unit has been given the characterizing features defined in the attached claims. More precisely, one characterizing feature of the invention is that the unit comprises two track stands, each of which comprises one track supported on two wheels and driven by one of the wheels, which stands are supported freely pivotally between the axles of their wheels each at the end of a rocker arm, which in its turn is supported freely pivotally between its ends on the drive axle of the vehicle, from which the respective track is driven via chain transmissions.
A vehicle equipped with track units according to the invention can be designed relatively narrow, without great risk of overturning when passing with one track unit over an obstacle, because the track stands of each unit move independently of the other track stand in the unit, and at the same time the rocker arm of the unit is permitted to pivot about its axis which thereby is caused to increase in height much less than the height of the obstacle.